The invention relates to a system for supplying inert gas to a multi-stage dry-running vacuum pump with systems for distributing the inert gas to the stages of the pump.
"Dry-running" vacuum pumps are pumps whose chambers contain no lubricant and/or sealing material. Typical pumps of this kind are multi-stage pumps and have rotary pistons of the claw type (Northey profile). Their advantage lies in the fact that they can produce vacuums completely free of hydrocarbons, so that they are used especially for the evacuation of vacuum chambers in which semiconductor processes (etching, coating or other vacuum treatment or manufacturing processes) are performed.
EP-A 365,695 (to which U.S. Pat. No. 5,046,934 corresponds) discloses a multi-stage dry-running vacuum pump of the kind herein concerned. It is provided with an inert gas supply which consists of a nitrogen source, conduit systems leading into the pump chambers, and a valve. In this previously known pump it cannot be determined whether the inert gas supply is functioning properly while the pump is operating. The object of the present invention is therefore to create a system of the kind referred to above, which can be checked during operation. The feeding of inert gas to the pump is intended, among other purposes, to prevent solid particles entering the pump or forming in the pump while the gases are being compressed from depositing themselves on the rotor or on the walls of the pumping chambers. Depending on the nature of the semiconductor process the inert gas requirement will differ not only in regard to the amount needed but also in regard to the point, i.e., the stage, at which the inert gas is needed. It must also be considered that the feeding of inert gas while the pump is running adversely affects the pump's output.
The present invention is therefore addressed to the additional task of creating a system of the kind referred to above by means of which not only can the inert gas feed be monitored, but also the nature of its distribution and its rates of flow can be influenced.